如何从UIImage(Cocoa Touch)或CGImage(Core Graphics)获取像素数据？

func getPixelDataFromUIImage(image: UIImage) -> UnsafeMutableRawPointer? {
    guard let cgImage = image.cgImage else {
        return nil
    }
    
    let width = Int(image.size.width)
    let height = Int(image.size.height)
    let bytesPerPixel = 4
    let bytesPerRow = width * bytesPerPixel
    let bitsPerComponent = 8
    
    let context = CGContext(data: nil,
                            width: width,
                            height: height,
                            bitsPerComponent: bitsPerComponent,
                            bytesPerRow: bytesPerRow,
                            space: CGColorSpaceCreateDeviceRGB(),
                            bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)
    
    guard let contextNonNull = context else {
        return nil
    }
    
    contextNonNull.draw(cgImage, in: CGRect(x: 0, y: 0, width: width, height: height))
    
    guard let pixelData = contextNonNull.data else {
        return nil
    }
    
    return pixelData
}